where would they find someone brave enough to go to someones door and say knock knock, can we steal you assault weapons?

They'll get them from the same place they found the ones who would kick in the door to take drugs, property, people, etc. If the locals won't do it, they'll import those who will from other areas, just as they did in New Orleans.

We expect officers to follow the law, even if they disagree with it. We expect a racist cop to protect all citizens, regardless of color. We expect a pro-life cop to protect Planned Parenthood offices. Why won't we expect cops to enforce gun control and gun bans, given they've been doing it since the first gun control was passed in Georgia in the 17th Century?